From 970812e39c236ff385e440ac6d458d196c237667 Mon Sep 17 00:00:00 2001 From: Johnothan King Date: Fri, 13 Jun 2025 16:29:15 -0700 Subject: [PATCH] Fix arbitrary command execution/code injection bugs (#866) * Security patch part 1 Never use $SHELL or sh.shpath when executing shebang-less scripts - sh_ntfork(): Removed a misguided optimization that causes ksh to run scripts without a shebang using the binary pointed to by either $SHELL or sh.shpath. This has a few problems: - The shell in sh.shpath or more disastrously in $SHELL has no guarantee of being identical to the currently running copy of ksh93 or even existing at all, so using either is not only bogus, but potentially dangerous. - The optimization has no ability to pass down the current POSIX mode status to the script. - It's only activated for virtual subshells, resulting in arbitrarily different behavior depending on whether or not we're in a virtual subshell. - It does some weird stuff with /dev/fd that seems superfluous, and also lacks any SHOPT_DEVFD if directive. (Additionally, if it did have one, that stat(2) would likely become mere dead code and a waste of context switches.) The optimization was probably intended to be used for running a shebang-less script via posix_spawn, which is ostensibly faster than fork. But this simply isn't possible without risking running the shebang-less script in a shell environment different from the current one. (If ksh were updated by the package manager while ksh is still running, this optimization would cause the script to run via the new version, rather than the currently running older version.) The optimization is unfixable by design, and as such must be removed to ensure correct behavior. * Security patch part 2 (re: bae02c39) rm setuid script code leading to arbitrary command execution Changes: - Delete code for setuid scripts on "Solaris 2.5+" because it allows for arbitrary command execution. One millisecond you think you're launching ksh, the next you're at the mercy of a hijacker. Example: SHELL=/bin/ppmflash /bin/ksh -l /dev/fd/0 < <(true) MANPATH: usage: MANPATH flashfactor [ppmfile] flashfactor: 0.0 = original picture, 1.0 = total whiteout The pathshell() code doesn't *seem* to be vulnerable to privilege escalation, but who knows (cf. CVE-2019-14868; this might need its own CVE 2025. Maybe pathshell() should be scrapped entirely???) - Add fickle but functional regression test (you may need to pass KSH=/bin/ksh or some such to get it to fail against vulnerable versions of ksh). The test uses a login shell via the -l option, but the bug *does not* need a login shell. See: https://github.com/ksh93/ksh/issues/874#issue-3128739066 Modify the execveat reproducer to pass along environ (which could include a hijacked SHELL), and you're in for a BAD time. Maybe the deleted code (introduced sometime within the period of 1995 and 1999) was relevant to some Solaris-specific use case or something. Maybe the erasure even causes an incompatibility. But that code must go; it's far too dangerous to execv whatever the hell pathshell gives us during **init**. (Need I bring CVE-2019-14868 back to remembrance again? This bug has similarities to that one.) FWIW, all of the regression tests in the ksh and modernish suites pass with this patch applied. * Security patch part 3 Delete pathshell() and replace uses of it with safer equivalents This function is a dangerous attack vector that ought not remain in the code base. The value returned by astconf() is doubtless safer than what is returned by pathshell(). * Other changes The libast pathprog function and prog feature test are now unused, and are removed. --- NEWS | 17 +++++ src/cmd/ksh93/include/shell.h | 3 - src/cmd/ksh93/sh/init.c | 33 +-------- src/cmd/ksh93/sh/main.c | 21 ------ src/cmd/ksh93/sh/path.c | 2 - src/cmd/ksh93/sh/xec.c | 20 ------ src/cmd/ksh93/tests/basic.sh | 28 ++++++++ src/cmd/ksh93/tests/posix.sh | 2 - src/lib/libast/Mamfile | 28 -------- src/lib/libast/comp/omitted.c | 2 +- src/lib/libast/comp/system.c | 48 ------------- src/lib/libast/features/prog | 12 ---- src/lib/libast/include/ast.h | 2 - src/lib/libast/man/compat.3 | 1 - src/lib/libast/man/path.3 | 13 ---- src/lib/libast/man/proc.3 | 5 +- src/lib/libast/misc/cmdarg.c | 2 +- src/lib/libast/misc/procopen.c | 2 +- src/lib/libast/path/pathprog.c | 124 -------------------------------- src/lib/libast/path/pathshell.c | 115 ----------------------------- 20 files changed, 52 insertions(+), 428 deletions(-) delete mode 100644 src/lib/libast/comp/system.c delete mode 100644 src/lib/libast/features/prog delete mode 100644 src/lib/libast/path/pathprog.c delete mode 100644 src/lib/libast/path/pathshell.c diff --git a/NEWS b/NEWS index f9b6e46..9e6bc6a 100644 --- a/NEWS +++ b/NEWS @@ -2,6 +2,23 @@ This documents significant changes in the 1.0 branch of ksh 93u+m. For full details, see the git log at: https://github.com/ksh93/ksh/tree/1.0 Uppercase BUG_* IDs are shell bug IDs as used by the Modernish shell library. +2025-06-14: + +- Fixed a bug occurring on systems with posix_spawn(3), spawnve(2), and + spawn(2), which when exploited could cause ksh93 to execute scripts + without a shebang with a shell other than itself, provided /bin/ksh + was hijacked, or in the case of ksh being unable to obtain it's own + executable path, whatever the SHELL variable was set to. + +- Fixed a bug that could cause scripts without a shebang to run + without POSIX mode enabled when executed in a virtual subshell. + +- Fixed a bug that could allow an attacker to hijack ksh93 during + shell initialization to execv a shell other than ksh itself, leading to + the ksh process being surreptitiously replaced with bash, zsh, or + really anything, provided the binary name ends with the letters + 'sh'. + 2024-08-01: - Release 1.0.10 -- exactly two years after 1.0.0 and twelve years after 93u+. diff --git a/src/cmd/ksh93/include/shell.h b/src/cmd/ksh93/include/shell.h index 96d982a..a7b090c 100644 --- a/src/cmd/ksh93/include/shell.h +++ b/src/cmd/ksh93/include/shell.h @@ -213,8 +213,6 @@ struct sh_scoped char **trapcom; /* EXIT and signals */ char **otrapcom; /* save parent EXIT and signals for v=$(trap) */ struct Ufunction *real_fun; /* current 'function name' function */ - int repl_index; - char *repl_arg; }; struct limits @@ -255,7 +253,6 @@ struct Shell_s Namval_t *bltin_nodes; Namval_t *bltin_cmds; History_t *hist_ptr; - char *shpath; char *user; char **sigmsg; char **login_files; diff --git a/src/cmd/ksh93/sh/init.c b/src/cmd/ksh93/sh/init.c index 1f1b71e..ab2ac66 100644 --- a/src/cmd/ksh93/sh/init.c +++ b/src/cmd/ksh93/sh/init.c @@ -1352,33 +1352,6 @@ Shell_t *sh_init(int argc,char *argv[], Shinit_f userinit) } /* increase SHLVL */ sh.shlvl++; -#if SHOPT_SPAWN - { - /* - * try to find the pathname for this interpreter - * try using environment variable _ or argv[0] - */ - char *cp=nv_getval(L_ARGNOD); - char buff[PATH_MAX+1]; - sh.shpath = 0; - if((n = pathprog(NULL, buff, sizeof(buff))) > 0 && n <= sizeof(buff)) - sh.shpath = sh_strdup(buff); - else if((cp && (sh_type(cp)&SH_TYPE_SH)) || (argc>0 && strchr(cp= *argv,'/'))) - { - if(*cp=='/') - sh.shpath = sh_strdup(cp); - else if(cp = nv_getval(PWDNOD)) - { - int offset = stktell(sh.stk); - sfputr(sh.stk,cp,'/'); - sfputr(sh.stk,argv[0],-1); - pathcanon(stkptr(sh.stk,offset),PATH_DOTDOT); - sh.shpath = sh_strdup(stkptr(sh.stk,offset)); - stkseek(sh.stk,offset); - } - } - } -#endif nv_putval(IFSNOD,(char*)e_sptbnl,NV_RDONLY); astconfdisc(newconf); #if SHOPT_TIMEOUT @@ -1391,7 +1364,6 @@ Shell_t *sh_init(int argc,char *argv[], Shinit_f userinit) #endif if(argc>0) { - int dolv_index; /* check for restricted shell */ if(type&SH_TYPE_RESTRICTED) sh_onoption(SH_RESTRICTED); @@ -1403,10 +1375,7 @@ Shell_t *sh_init(int argc,char *argv[], Shinit_f userinit) sh_done(0); } opt_info.disc = 0; - dolv_index = (argc - 1) - sh.st.dolc; - sh.st.dolv = argv + dolv_index; - sh.st.repl_index = dolv_index; - sh.st.repl_arg = argv[dolv_index]; + sh.st.dolv = argv + (argc - 1) - sh.st.dolc; sh.st.dolv[0] = argv[0]; if(sh.st.dolc < 1) { diff --git a/src/cmd/ksh93/sh/main.c b/src/cmd/ksh93/sh/main.c index 7acce0a..3ec360e 100644 --- a/src/cmd/ksh93/sh/main.c +++ b/src/cmd/ksh93/sh/main.c @@ -243,33 +243,12 @@ int sh_main(int ac, char *av[], Shinit_f userinit) /* open stream should have been passed into shell */ if(strmatch(name,e_devfdNN)) { -#if !_WINIX - char *cp; - int type; -#endif fdin = (int)strtol(name+8, NULL, 10); if(fstat(fdin,&statb)<0) { errormsg(SH_DICT,ERROR_system(1),e_open,name); UNREACHABLE(); } -#if !_WINIX - /* - * try to undo effect of Solaris 2.5+ - * change for argv for setuid scripts - */ - if(sh.st.repl_index > 0) - av[sh.st.repl_index] = sh.st.repl_arg; - if(((type = sh_type(cp = av[0])) & SH_TYPE_SH) && (name = nv_getval(L_ARGNOD)) && (!((type = sh_type(cp = name)) & SH_TYPE_SH))) - { - av[0] = (type & SH_TYPE_LOGIN) ? cp : path_basename(cp); - /* exec to change $0 for ps */ - execv(pathshell(),av); - /* exec fails */ - sh.st.dolv[0] = av[0]; - fixargs(sh.st.dolv,1); - } -#endif name = av[0]; sh_offoption(SH_VERBOSE); sh_offoption(SH_XTRACE); diff --git a/src/cmd/ksh93/sh/path.c b/src/cmd/ksh93/sh/path.c index 2e0f76e..06bf66f 100644 --- a/src/cmd/ksh93/sh/path.c +++ b/src/cmd/ksh93/sh/path.c @@ -1196,8 +1196,6 @@ pid_t path_spawn(const char *opath,char **argv, char **envp, Pathcomp_t *libpath */ if(spawn) { - if(sh.subshell) - return -1; do { if((pid=fork())>0) diff --git a/src/cmd/ksh93/sh/xec.c b/src/cmd/ksh93/sh/xec.c index dd56905..8f82792 100644 --- a/src/cmd/ksh93/sh/xec.c +++ b/src/cmd/ksh93/sh/xec.c @@ -3395,26 +3395,6 @@ static pid_t sh_ntfork(const Shnode_t *t,char *argv[],int *jobid,int topfd) job_fork(-1); jobfork = 1; spawnpid = path_spawn(path,argv,arge,pp,(grp<<1)|1); - if(spawnpid < 0 && errno==ENOEXEC) - { - char *devfd; - int fd = open(path,O_RDONLY); - argv[-1] = argv[0]; - argv[0] = path; - if(fd>=0) - { - struct stat statb; - sfprintf(sh.strbuf,"/dev/fd/%d",fd); - if(stat(devfd=sfstruse(sh.strbuf),&statb)>=0) - argv[0] = devfd; - } - if(!sh.shpath) - sh.shpath = pathshell(); - spawnpid = path_spawn(sh.shpath,&argv[-1],arge,pp,(grp<<1)|1); - if(fd>=0) - close(fd); - argv[0] = argv[-1]; - } fail: if(jobfork && spawnpid<0) job_fork(-2); diff --git a/src/cmd/ksh93/tests/basic.sh b/src/cmd/ksh93/tests/basic.sh index 49f4f41..5c034e3 100755 --- a/src/cmd/ksh93/tests/basic.sh +++ b/src/cmd/ksh93/tests/basic.sh @@ -1016,5 +1016,33 @@ do done unset testcode +# ====== +# Hijacking ksh93 via $SHELL for arbitrary command execution during initialization. +# https://github.com/ksh93/ksh/issues/874 +bindir=$tmp/dir.$RANDOM/bin +mkdir -p "$bindir" +echo $'#!/bin/sh\necho "CODE INJECTION"' > "$bindir"/hijack_sh +chmod +x "$bindir"/hijack_sh +got=$(set +x; SHELL="$bindir"/hijack_sh "$SHELL" -l <(echo) 2>&1) +[[ $got =~ "CODE INJECTION" ]] && err_exit 'ksh93 is vulnerable to being hijacked during init via $SHELL' \ + "(got $(printf %q "$got"))" + +# Hijacking ksh93 shebang-less scripts for arbitrary command execution. +# https://github.com/ksh93/ksh/pull/866 +export bindir +print 'echo GOOD' > "$bindir/dummy.sh" +chmod +x "$bindir/dummy.sh" +cp "$SHELL" "$bindir/hijack_sh" +exp=$'GOOD\nGOOD' +got=$("$bindir/hijack_sh" -c $'print $\'\#!/bin/sh\necho HIJACKED\' > "$bindir/hijack_shell" +chmod +x "$bindir/hijack_shell" +rm "$bindir/hijack_sh" +cp "$bindir/hijack_shell" "$bindir/hijack_sh" +("$bindir/dummy.sh"); "$bindir/dummy.sh"; :') +rm -r "$bindir" +unset bindir +[[ $exp == $got ]] || err_exit 'ksh93 shebang-less scripts are vulnerable to being hijacked for arbitrary code execution' \ + "(exp $(printf %q "$exp"), got $(printf %q "$got"))" + # ====== exit $((Errors<125?Errors:125)) diff --git a/src/cmd/ksh93/tests/posix.sh b/src/cmd/ksh93/tests/posix.sh index f72dac9..54a8ed3 100755 --- a/src/cmd/ksh93/tests/posix.sh +++ b/src/cmd/ksh93/tests/posix.sh @@ -83,7 +83,6 @@ got=$(|out got=$( * -* David Korn * -* Phong Vo * -* Martijn Dekker * -* Johnothan King * -* * -***********************************************************************/ -/* - * AST library system(3) - */ - -#define system ______system - -#define _STDLIB_H_ 1 /* UWIN workaround */ - -#include -#include - -#undef system - -#undef _def_map_ast -#include - -extern int -system(const char* cmd) -{ - char* sh[4]; - - if (!cmd) - return !eaccess(pathshell(), X_OK); - sh[0] = "sh"; - sh[1] = "-c"; - sh[2] = (char*)cmd; - sh[3] = 0; - return procrun(NULL, sh, 0); -} diff --git a/src/lib/libast/features/prog b/src/lib/libast/features/prog deleted file mode 100644 index 365ce88..0000000 --- a/src/lib/libast/features/prog +++ /dev/null @@ -1,12 +0,0 @@ -lib getexecname,_NSGetExecutablePath - -tst run{ - for p in /proc/self/exe /proc/self/path/a.out - do if test -e $p - then echo "#define _PROC_PROG \"$p\"" - break - fi - done -}end - -_hdr_macho_o_dyld = hdr mach-o/dyld diff --git a/src/lib/libast/include/ast.h b/src/lib/libast/include/ast.h index 1f9aa90..8cc5b6e 100644 --- a/src/lib/libast/include/ast.h +++ b/src/lib/libast/include/ast.h @@ -364,11 +364,9 @@ extern size_t pathnative(const char*, char*, size_t); extern char* pathpath(char*, const char*, const char*, int); extern char* pathpath_20100601(const char*, const char*, int, char*, size_t); extern size_t pathposix(const char*, char*, size_t); -extern size_t pathprog(const char*, char*, size_t); extern char* pathrepl(char*, const char*, const char*); extern char* pathrepl_20100601(char*, size_t, const char*, const char*); extern int pathsetlink(const char*, const char*); -extern char* pathshell(void); extern char* pathtemp(char*, size_t, const char*, const char*, int*); extern char* pathtmp(char*, const char*, const char*, int*); extern char* setenviron(const char*); diff --git a/src/lib/libast/man/compat.3 b/src/lib/libast/man/compat.3 index 8fb5d06..02d4df6 100644 --- a/src/lib/libast/man/compat.3 +++ b/src/lib/libast/man/compat.3 @@ -57,7 +57,6 @@ int rmdir(const char*); int sigunblock(int); double strtod(const char*, char**); long strtol(const char*, char**, int); -int system(const char*); char* tmpnam(char*); int unlink(const char*); .EE diff --git a/src/lib/libast/man/path.3 b/src/lib/libast/man/path.3 index f44142f..e13d697 100644 --- a/src/lib/libast/man/path.3 +++ b/src/lib/libast/man/path.3 @@ -56,7 +56,6 @@ char* pathnext(char* \fIpath\fP, char* \fIextra\fP, long* \fIvisits\fP); char* pathpath(char* \fIpath\fP, const char* \fIp\fP, const char* \fIa\fP, int \fImode\fP); char* pathrepl(char* \fIpath\fP, const char* \fImatch\fP, const char* \fIreplace\fP); int pathsetlink(const char* \fItext\fP, char* \fIname\fP); -char* pathshell(void); int pathstat(const char* \fIpath\fP, struct stat* \fIst\fP); char* pathtemp(char* \fIpath\fP, const char* \fIdir\fP, const char* \fIpfx\fP); .EE @@ -323,18 +322,6 @@ above for weird .IR universe (1) interactions hidden by this routine. .PP -.L pathshell -returns a pointer to the pathname for the shell for the current process. -The -.L SHELL -environment variable is first consulted, but is rejected under suspicious -ownership/setuid conditions of if it seems to point to -.IR csh (1) ; -otherwise -.L confstr(_CS_SHELL,...) -is used. -A valid string is always returned. -.PP .L pathstat first tries .LI stat( path,st ) diff --git a/src/lib/libast/man/proc.3 b/src/lib/libast/man/proc.3 index a338130..9aa66e9 100644 --- a/src/lib/libast/man/proc.3 +++ b/src/lib/libast/man/proc.3 @@ -80,8 +80,9 @@ If .I command is .L 0 -then the current shell is used (see -.IR pathshell (3)). +then the shell returned by +.IR astconf (3) +is used. If .I envv is not diff --git a/src/lib/libast/misc/cmdarg.c b/src/lib/libast/misc/cmdarg.c index bb4a4e3..6f8b24f 100644 --- a/src/lib/libast/misc/cmdarg.c +++ b/src/lib/libast/misc/cmdarg.c @@ -128,7 +128,7 @@ cmdopen_20120411(char** argv, int argmax, int size, const char* argpat, Cmddisc_ x = ARG_MAX; if (size <= 0 || size > x) size = x; - sh = pathshell(); + sh = astconf("SH", NULL, NULL); m = n + (argc + 4) * sizeof(char**) + strlen(sh) + 1; m = roundof(m, sizeof(char**)); if (size < m) diff --git a/src/lib/libast/misc/procopen.c b/src/lib/libast/misc/procopen.c index 5cecfd2..a6b396b 100644 --- a/src/lib/libast/misc/procopen.c +++ b/src/lib/libast/misc/procopen.c @@ -719,7 +719,7 @@ procopen(const char* cmd, char** argv, char** envv, long* modv, int flags) *p = path; *--p = "sh"; } - strcpy(env + 2, (flags & PROC_PARANOID) ? astconf("SH", NULL, NULL) : pathshell()); + strcpy(env + 2, astconf("SH", NULL, NULL)); if (forked || (flags & PROC_OVERLAY)) execve(env + 2, p, environ); #if _use_spawnveg diff --git a/src/lib/libast/path/pathprog.c b/src/lib/libast/path/pathprog.c deleted file mode 100644 index 09a6148..0000000 --- a/src/lib/libast/path/pathprog.c +++ /dev/null @@ -1,124 +0,0 @@ -/*********************************************************************** -* * -* This software is part of the ast package * -* Copyright (c) 1985-2012 AT&T Intellectual Property * -* Copyright (c) 2020-2023 Contributors to ksh 93u+m * -* and is licensed under the * -* Eclipse Public License, Version 2.0 * -* * -* A copy of the License is available at * -* https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.html * -* (with md5 checksum 84283fa8859daf213bdda5a9f8d1be1d) * -* * -* Glenn Fowler * -* David Korn * -* Phong Vo * -* Martijn Dekker * -* * -***********************************************************************/ -/* - * Glenn Fowler - * AT&T Research - * - * return the full path of the current program in path - * command!=0 is used as a default - */ - -#include - -#if _WINIX -#include -#include -#endif - -#include "FEATURE/prog" - -#if _hdr_macho_o_dyld && _lib__NSGetExecutablePath -#include -#else -#undef _lib__NSGetExecutablePath -#endif - -static size_t -prog(const char* command, char* path, size_t size) -{ - ssize_t n; - char* s; -#if _WINIX - char* t; - char* e; - int c; - int q; -#endif -#if _lib__NSGetExecutablePath - uint32_t z; -#endif - -#ifdef _PROC_PROG - if ((n = readlink(_PROC_PROG, path, size)) > 0 && *path == '/') - { - if (n < size) - path[n] = 0; - return n; - } -#endif -#if _lib_getexecname - if ((s = (char*)getexecname()) && *s == '/') - goto found; -#endif -#if _lib__NSGetExecutablePath - z = size; - if (!_NSGetExecutablePath(path, &z) && *path == '/') - return strlen(path); -#endif -#if _WINIX - if (s = GetCommandLine()) - { - n = 0; - q = 0; - t = path; - e = path + size - 1; - while (c = *s++) - { - if (c == q) - q = 0; - else if (!q && c == '"') - q = c; - else if (!q && isspace(c)) - break; - else if (t < e) - *t++ = c == '\\' ? '/' : c; - else - n++; - } - if (t < e) - *t = 0; - return (t - path) + n; - } -#endif - if (command) - { - s = (char*)command; - goto found; - } - return 0; - found: - n = strlen(s); - if (n < size) - memcpy(path, s, n + 1); - return n; -} - -size_t -pathprog(const char* command, char* path, size_t size) -{ - char* rel; - ssize_t n; - - if ((n = prog(command, path, size)) > 0 && n < size && *path != '/' && (rel = strdup(path))) - { - n = pathpath(rel, NULL, PATH_REGULAR|PATH_EXECUTE, path, size) ? strlen(path) : 0; - free(rel); - } - return n; -} diff --git a/src/lib/libast/path/pathshell.c b/src/lib/libast/path/pathshell.c deleted file mode 100644 index 7537c53..0000000 --- a/src/lib/libast/path/pathshell.c +++ /dev/null @@ -1,115 +0,0 @@ -/*********************************************************************** -* * -* This software is part of the ast package * -* Copyright (c) 1985-2011 AT&T Intellectual Property * -* Copyright (c) 2020-2023 Contributors to ksh 93u+m * -* and is licensed under the * -* Eclipse Public License, Version 2.0 * -* * -* A copy of the License is available at * -* https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.html * -* (with md5 checksum 84283fa8859daf213bdda5a9f8d1be1d) * -* * -* Glenn Fowler * -* David Korn * -* Phong Vo * -* Martijn Dekker * -* Johnothan King * -* * -***********************************************************************/ -/* - * G. S. Fowler - * D. G. Korn - * AT&T Bell Laboratories - * - * shell library support - */ - -#include -#include - -/* - * return pointer to the full path name of the shell - * - * SHELL is read from the environment and must start with / - * - * if setuid or setgid then the executable and its containing - * directory must not be owned by the real user/group - * - * root/administrator has its own test - * - * astconf("SH",NULL,NULL) is returned by default - * - * NOTE: csh is rejected because the bsh/csh differentiation is - * not done for `csh script arg ...' - */ - -#ifdef _WINIX -# define EXE "?(.exe)" -#else -# define EXE -#endif - -char* -pathshell(void) -{ - char* sh; - int ru; - int eu; - int rg; - int eg; - struct stat st; - - static char* val; - - if ((sh = getenv("SHELL")) && *sh == '/' && strmatch(sh, "*/(sh|*[!cC]sh)*([[:digit:]])?(-+([.[:alnum:]]))" EXE)) - { - if (!(ru = getuid()) || !eaccess("/bin", W_OK)) - { - if (stat(sh, &st)) - goto defshell; - if (ru != st.st_uid && !strmatch(sh, "?(/usr)?(/local)/?([ls])bin/?([[:lower:]])sh" EXE)) - goto defshell; - } - else - { - eu = geteuid(); - rg = getgid(); - eg = getegid(); - if (ru != eu || rg != eg) - { - char* s; - char dir[PATH_MAX]; - - s = sh; - for (;;) - { - if (stat(s, &st)) - goto defshell; - if (ru != eu && st.st_uid == ru) - goto defshell; - if (rg != eg && st.st_gid == rg) - goto defshell; - if (s != sh) - break; - if (strlen(s) >= sizeof(dir)) - goto defshell; - strcpy(dir, s); - if (!(s = strrchr(dir, '/'))) - break; - *s = 0; - s = dir; - } - } - } - return sh; - } - defshell: - if (!(sh = val)) - { - if (!*(sh = astconf("SH", NULL, NULL)) || *sh != '/' || eaccess(sh, X_OK) || !(sh = strdup(sh))) - sh = "/bin/sh"; - val = sh; - } - return sh; -} -- 2.50.1